* chore: split deps into separate extras

* chore: update docs and dockerfile

* chore: only install vectorizer-worker extra in dockerfile

The vectorizer worker used to process queue items in a single
transaction. If any step (other than file loading) failed, it would
cause the processing to abort, and later be retried. Because it operated
in a single transaction, it did not record failed attempts in the queue
table.

This change rearchitects the queue item processing to consist of two
transactions:
- The "fetch work" transaction gets a batch of rows from the database
  for processing. It updates the `attempts` column of those rows to
  signal that an attempt has been made to process the item. It deletes
  duplicate queue items for the same primary key columns.
- The "embed and write" transaction performs embedding, writes the
  embeddings to the database, and removes successfully processed queue
  rows. Rows which failed to be processed have the `retry_after` column
  set to a value proportional to the number of existing attempts. When
  the `attempts` column goes over a predefined threshold (6), the queue
  item is moved to the "failed" (dead letter) queue.

There is no FK from the queue table to the source table, or from the
embedding table to the source table. As a result, we can have "dangling"
entries in both the queue table and the embedding table. These occur
because of a race condition between deleting a source table row, and the
processing of the embeddings for that row.

To "clean up" dangling embeddings, we insert a queue row when a source
table row is deleted. This queue row is dangling.

When a dangling queue row is identified, we use the PK values of the
queue row to remove all associated embeddings (if present).

Co-authored-by: Jascha <[email protected]>